The invention relates to the use of ethylenediamine tetraacetic acid (further on: EDTA) and its derivatives, i.e. its salts and complexes for prevention and treatment of bacterial intestinal diseases of pigs and for increasing the effects of antibiotics exerted in such diseases. The invention also relates to compositions for animal husbandry comprising EDTA or its derivatives. The term “composition for animal husbandry” encompasses both veterinary compositions and feeds and drinks which can be consumed by pigs, such as fodders, feeds, nutriments, pre-mixes and drinking water additives.
Of the bacterial diseases of pigs pig dysentery is the one which causes the most serious problems. Pig dysentery is an epizootic disease of piglets and grown-up pigs involving mucous-bloody diarrhoea and furfuraceous necrosis of colonic mucous membrane.
Pig dysentery belongs to diseases which frequently occur all over the world. Due to the direct losses and to the high costs of therapy this disease causes considerable economic damages. The causative pathogen of the disease is Brachyspira hyodysenteriae, previously also termed as Treponema hyodysenterae or Serpulina hyodysenteriae. The resistance of the pathogen is low; it dies within some minutes at temperatures exceeding 60° C. and upon the effect of conventional disinfecting agents and it dies within some days upon drying. However, the bacteria remain viable in the mucous-bloody faeces in summer for at least one week and in winter even for about two months. In thin manure which forms in large amounts at pig farms, the pathogen may be viable even for some months. Pigs are susceptible to the pathogen, moreover the pathogen may also accumulate in the intestines of rats, mice and dogs living at the infected farm. The pathogen is excreted by rats for some days, by dogs for some weeks, and mice may excrete the pathogen even for some months.
The disease is observed generally on pigs older than 6-8 weeks, because suckling pigs have usually maternal immunity. Immunity developed in older pigs is poor and partial. Upon a massive re-infection or as a result of farming anomalies the disease may re-develop on one and the same livestock. Despite the acquired relative immunity, most of the once-recovered pigs remain carriers and excreters of the pathogen even during their entire lifespan.
The pathogen binds to the surface of intestinal endothelial cells but does not enter them. The toxins which liberate from the bacteria damage the endothelial cells of the mucous membrane, as a result of which the endothelial cells die and inflammation sets in. This inflammation induces excessive mucus production, bleeding occurs, liquid is excreted into the intestinal cavities, a severe diarrhoea sets in, the absorption potential of the intestines is severely impaired, followed by the necrosis of the surface layer of the intestinal mucous membrane. The lesions are throughout restricted to the colon.
The latency period is 10-14 days. The first symptom is a water-like diarrhoea coupled with subfebrility and lack of appetite. After some days blood and fibrin shreds also appear in the faeces. At this time faeces is already chocolate brown. The animals get weakened, they do not eat only drink, and their body weight rapidly decreases. Many of the animals die; the perishment ratio may be as high as 30%. Although the majority of the sick animals recovers, their development gets retarded and they continue to excrete the pathogen.
Beside the characteristic symptoms, necropsy usually shows a repleted stomach and a swollen hyperaemic mucous membrane covered with phlegm. The mucous membrane of the colon is swollen, bright red, particularly at the edges of the folds, and has a velvet-like surface. At a later stage a furfuraceous deposit appears due to the necrosis of the surface of the mucous membrane.
Numerous veterinary substances and compositions have already been used for the treatment of bacterial intestinal disesases of pigs, particularly of pig dysentery. Examples of them are various sulfonamides, benzene-acetonitrile, benzoic acid, pyridine, quinoline, pyrimidine and guanidine derivatives, as well as ionophoric antibiotics which have become increasingly frequent in the last decades. The use of some of the known active agents which proved to be effective, thus e.g. carbadox and dimetridazole, is nowadays not allowed due to the long stay periods prescribed by food hygienics and/or due to the disadvantages to human health detected in the meanwhile. The pathogen develops resistance relatively quickly against some active agents, particularly against guanidine derivatives and antibiotics. As a particular problem, the known active agents can frequently be used only for the treatment of an already established disease but not for prevention, or if yes, their prolonged use lays an undue burden on the animal organism and sometimes runs with undesired side effects. Vaccination did not prove to be successful against the disease.